PIP joints, such as those of the hands or feet, can be damaged by trauma, injury and/or by disease such as osteoarthritis, such that the joint is no longer viable. PIP joints differ from other joints in that the range of motion occurs generally within a single plane, e.g. flexion without significant lateral rotation that occurs with other joints, such as with a shoulder or a hip. A healthy range of motion includes 0-5 degrees in extension to 100-115 degrees in flexion. A functional range of motion is 36-86 degrees in flexion, and an acceptable outcome for PIP arthroplasty is 50-70 degrees in flexion.
Existing replacement joints or prostheses typically are integrated devices which includes an affixed attachment mechanism glued and/or located in a medullary canal of the bone. The opposing faces of the bones, such as ends of the phalanges are removed to create a stable supporting surface through which an opening is made into the medullary canal parallel to the length of the bone. Deformities in the bone are also typically removed. Direct attachment of the replacement joint to the bone makes revision, i.e. replacement of the prosthesis, in instances of replacement joint failure difficult and can further damage the surrounding tissue.
Due to the stresses placed on the joint, insufficient lateral stability, and expected implant survival rates, one alternative approach to PIP replacement is to fuse the joint rather than replace the joint. This is often the procedure for younger patients, which have expected survival rates beyond what is currently offered in replacement joints. Patient satisfaction with current prostheses is considerably less than hip and knee arthroplasties. PIP arthroplasties are typically used to alleviate debilitating joint pain and/or deformity. Current approaches are moderately successful in alleviating pain and restoring cosmetic appearance, but are prone to failure and maintain only a nominal range of motion.
Arthroplasties are typically planned prior to a replacement with a specific range of replacement sizes ordered in advance, and the replacement joint selected based on external measurements, medical imaging, and external visual observation. Tissue damage including both the bone and surrounding tissue can be difficult to assess prior to the operative procedure. Soft tissues play a considerable role in lateral support of interphalangeal joints. Prostheses are manufactured according to various sizes and the range of sizes limited by cost, e.g. more sizes available to choose from means more devices produced than needed, and fewer sizes are limited by proper functioning of the prostheses in terms of range of motion, gripping strength, lateral stability, etc.
Dissatisfaction with existing PIP replacement joints includes failure due to mechanical failure, dislocation, and/or limited range of motion. Mechanical failures, such as fracturing of the implanted joint, can occur due to repetitive motion and stresses placed on the joint. Dislocation occurs where the connection between an attachment mechanism of the replacement joint and a canal in the bone tissue dislocate or separate. The dislocation can include a loosening of the replacement joint and migration in the canal of the bone. The loosening and migration can further damage surrounding tissue and affect continued viability of the joint operation.